Remove `__init__.py` in custom_ops directory

[facaiy]

When reviewing #140, I find we forget to remove init python file in tensorflow_addons/custom_ops?
https://github.com/tensorflow/addons/blob/master/tensorflow_addons/custom_ops/__init__.py

cc @seanpmorgan Sean, what do you think?

[seanpmorgan]

Yes no need for this file. As you mention its leftover from the custom op re-org